Filter



Patented Nov. I15, 1927.

UNITED STATES JOSEF HERMANN ANI) MAX STAUBER, OF COLOGNE, GERMANY.

FILTER.

Application med April 24, 1924, Serial o. 708,734, and in Germany May 22, 1923.

Our invention refers to iltration and it more particularly concerns the filtration of liquids by means of silicio acid (SiO2 It is an object of our invention to provide means for effecting the filtration with the aid of silicic acid in a more perfect and economic manner than has hitherto been possible.

It is well known to free liquids of substances dissolved therein by filtration with the aid of silicio acid, but uptill now this material has been used only in pulverized form in order to offer the llargest possible surface area. The use of such filtering material involves the disadvantage of requiring permanent stirring and, in order to avoid losses of the liquid to be filtered, the silicio acid, after its ltering power is exhausted, must be freed from the liquid by extraction. inasmuch now as the silicio acid is employed in pulverized form, this operation is connected with great diiiiculties, and it has therefore been necessary to employ presses,

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separators, rotary extraction apparatuses and the like, requiring a great expenditure of power, attendance and installation. The unavoidable losses of solvent also form an important factor.

It is possible, of course, to restore to the pulverized silicic acid its iltering power by -distilling and calcining, but there again separate apparatuses are required for each operation.

A further material disadvantage consists therein that a smaller or larger quantity of the pulverized material will frequently be carried along by the liquid and, for instance in thevcase of lubricating oil, the ne powder will work damage in machinery and the like.

According to the present invention, we eifect filtration by means of more or yless coarsely vgrained silicio acid which is obtained by shaping and thereafter drying silicio acid gel containing less than 91 per cent water. The silicio acid gel can for inf stance be produced in a manner well known per se by mixing a dilute mineral acid such as for instance hydrochloric acid with n sodium silicate until a neutral reaction is obtained, the concentration of the components being vso chosen that the resulting liquid mixture contains from 5 to 10 per cent SiOg. After some time this liquid m1xture will set as a firm jelly-like mass orgel, which after having been comminuted in some suitable manner is then washed with water. The silica gel thus obtained is then shaped, by pressure or otherwise, into coarse grains or into rods which are broken up to form coarse grains, the granular material containing less than 91 per cent water and being now dried 60 at temperatures between 1GO-200 C. By first shaping silica gel containing not more than 91 per cent water and drying the shaped material, a silica gel is imparted particularly advantageous adsorptive properties. The filtering eect of the grained silicio acid thus obtained is surprising and at least equal to that of pulverized silicic acid. Raw dark colored mineral oil distillates are converted by means of grained silicio acid into light colored reiined products which can further be converted into high grade products. By the novel mode of filtration for instance the well known refining process by means of sulphuric acid and caustic soda, which is so clumsy and which entails heavy losses, can be rendered superiuous either partly or entirely.

This result could not be expected, inasmuch as the present invention conflicts with the present day ideas, according to which th`e filtering means must be 'emplo ed in the inest possible form, preferably 1n colloidal form, in order to offer a larger surface area. The great advantage offered by the use of grained silicio acid consists, among others, in the low resistance which it offers to the passage of the liquid to be filtered. If pulverized material is used, it is necessary to permanently stir with great energy during ltration. In contradistinction thereto, filtration through lgrained silicio acid can be carried out without any mechanical movement. Moreover, in the present case, the filtrate is ready for direct use, while a filtrate which passes through pulverized material must be subjected to comparatively high pressure, a great amount of ltering cloths being spent 'in this operation.

A further advantage offered by the invention consists therein that the filtering material, after its filtering power is exhausted, can easily be regenerated, it being possible to regenerate grained silicio acid in the filtering apparatus itself, for instance by boiling with water, b-y the action of steam, by calcining, extraction and the like with subsequent drying. Thus, by usine silicio acid obtained in the manner described, a great technical advantage is obtained by the great saving in power, time and apparat-uses.

Filtration by means of grained silicio acid is carried out, for instance, by supplying the liquid to be filtered by way of a collecting chamber to one or several pressure tubes in which the liquid rises until it fiows over the upper ends of the tubes and from there downwards through the mass of more or less coarsely grained silicic acid contained in the annular space between the tubes and 'the jackets surrounding them, the filtrate escaping at the bottom of the jackets ready for use. This filtering device can be permanently mounted within a refractory chamber adapted to be heated, so that it is possible to effect the regeneration of the filtering material by steaming or by calcination in the filtering device itself, whereby all stirring devices, filter presses, suction filters, distilling and calcining` ovens and the like can be dispensed with altogether.

In the drawings affixed to this specification and forming part thereof, a filtering device fit for use in practising my invention. and forming itself part thereof, is illustrated diagrammatically by way of example in vertical section.

Referring to the drawing, a is the liquid supply pipe and b is the collecting chamber. The liquid supplied to b through a rises in the tubes c, which may be provided in any desired number and are surrounded by jackets d1, d2, (Z3. The annular spaces confined between the tubes and the jackets are filled almost up to the upper ends of the tubes with the more or less coarsely grained filtering material e. Strainers f or the like at the bottom of the jackets prevent the material from dropping out. The liquid rising in the tubes c1, c, c3 flows over the upper edges of the tubes and then downwards through the filtering material e, collecting in the chamber a above the bottom b, being tapped olf at g. No stirring is required during filtration, the liquid flowing through the filtering material, owing to the great permeability of this latter under the action of its own gravity, so that the clear filtrate is obtained in an uninterrupted operation which can be regulated in a well known manner by suitable throttling means.

By arranging the filtering device substani tially as described, the filters 'can be enclosed entirely; they can be made of refractory material and can be enclosed in a refractory valve o, the natural draught causing t chamber adapted to be heated. By this arrangement the regeneration of the filtering material described further below can be carried out -in the filters themselves.

As shown in the drawings, the filters consisting each of a jacket d, tube c and filtering material e are all enclosed in a refractory chamber h, arranged after the manner of a heating oven and provided with some suitable kind of furnace e', a chimney 7c and an air valve 0. When the filtering power of the material e 1s exhausted after some time, which usually will be about twenty hours, the. mass is acted upon in the following manner First of all, the rest of filtrate which is still present in the tubes c is tapped off through pipe Z. The furnace is now heated and the filters are subjected to such temperature that part of the foreign matter within the mass 1s expelled by distillation, while the steam injected through pipe m, in order to further distillation, is prevented from condensing. The steam acts towards expelling the foreign matter still present in the filtering material which is condensed in the cooler n inserted in the pipe Z. When nothing but water escapes from pipe Z, the regeneration of the filtering material is finished and the injection of steam is stopped.

In the apparatus illustrated in the drawing, the steam pipe m ends in an annular pipe having a great number of perforations which act towards distributing the steam over the tubes c. However, steam can also be supplied in any other suitable manner, it being merely essential that its temperature be lower than the temperature of the heating material, in order that the steam be prevented from condensinoi and the ltering material remai-n dry. fter cooling down, the filtering material is ready for use again. Cooling is preferably effected by introducing fresh air into the chamber througlh the e hot air to pass through the chamber and to escape at s.

Obviously the regeneration with the aid of steam as above described will not suffice'to remove all traces of foreign matter from the filtering material and it is therefore possible to clean this material from time to time by calcination. This can also be effected in a simple manner by discontinuing the injection of steam used for regeneration and thereafter raising the temperature in the chamber to such an extent that the carbo=. naceous matter still present in the filtering material e is burnt entirely with the aid of fresh air introduced at p, the gases of combustion escaping at g.

The term coarsely grained as used in this specification and in the claims appended to it is intended to include grains of all sizes which in their totality do not form a, powder.

lll?) 6 skilled in the art.

1. The method of preparing filtering material comprising acting on a silica gel containing less than 91 per cent water so as to l0 shape it into coarse grains before drying same and only thereafter drying the granular material.

2. The method of filtering a liquid comprising bringing such liquid into contact with coarsel grained silica gel obtained according to t e method claimed in claim 1.

In testimony whereof we aix our signatureso JOSEF HERRMANN. MAX STAUBER. 

